The color of flower is a particularly important character in ornamental plants, and flowers having various colors have been produced by cross breeding heretofore. However, in the case of the cross breeding, gene sources are limited to species which are capable of cross breeding, and colors to be changed are limited. Further, in a case where only a specific character such as flower color is introduced into a specific variety, it is necessary to repeat backcrossing for long generations, and a lot of effort and time are required. Further, a period of cross breeding varies depending on plant species, and some plants take from a few years to a few decades for blossom. Particularly, Orchids such as moth orchid and cymbidium require a long time for blossom, and it takes a long time to develop such plants. Therefore, although demanded in markets, a superior new variety of moth orchid or cymbidium having a new flower color, particularly blue flower, has not been produced.
In recent years, it is possible to carry out cross breeding over species or genus by the recombinant DNA technology, and it is expected to produce a new variety having a color which cannot be obtained by the conventional cross breeding.
The color of flower derives mainly from three types of pigments: anthocyanin, carotenoid and betalain. Among them, anthocyanin (from orange to blue color) having the broadest maximum absorption wavelength has a role to govern blue color. Anthocyanin is one of flavonoids and biologically synthesized through a metabolic pathway shown in FIG. 1. The color of anthocyanin substantially depends on its chemical structure, and the more the number of hydroxyl groups in a benzene ring is, the more the color becomes blue. The hydroxylation of the benzene ring is catalyzed by a flavonoid 3′-hydroxylase (F3′H) and a flavonoid 3′,5′-hydroxylase (F3′5′H). In a case where there is neither F3′H activity nor F3′5′H activity in petal cells, pelargonidin (from orange color to red color) is synthesized, and in a case where there is F3′H activity, cyanidin (from red to crimson color) is synthesized. Further, in a case where there is F3′5′H activity, delphinidin (blue color) is synthesized. Therefore, in order to produce the blue flower color, the role of F3′5′H is considered to be important.
From such a viewpoint, a study is in progress to produce a plant having a blue flower by the gene recombination using F3′5′H.
As conventionally known genes encoding the F3′5′H, genes derived from plants such as Campanula medium, Catharanthus roseus, Petunia, Eustoma grandiflorum, Nierembergia sp., Verbena, Gentiana, Gossypium hirsutum, Lycianthes rantonnei, Solanum tuberosum and Torenia, have been known, however, a gene encoding the F3′5′H which is isolated from a Commelina communis has not been reported.
As examples wherein a flower color is changed by using a conventionally known gene, a method for producing a blue carnation by transfecting a carnation DFR (dihydroflavonol 4-reductase) deficient variety with a F3′5′H gene and DFR gene which are derived from Petunia (Patent Document 1) and a method for producing a blue rose by transfecting a rose of which internal metabolism pathway is suppressed, with a F3′5′H gene derived from Viola×wittrockiana (Patent Document 2) have been reported.
On the other hand, it has been reported to change the flower color of moth orchid by overexpressing an endogenous gene, however, a blue moth orchid has not been produced (Non-Patent Document 1). Further, it has not been reported to have produced a blue variety of cymbidium.    Patent Document 1: WO1996/036716    Patent Document 2: WO2005/017147    Non-Patent Document 1: Su and Hsu, Biotechnology Letters (2003) 25: 1933-1939.